SUMMARYFive sheep under halothane anesthesia were prepared with bilateral transit time ultrasonic flow probes around the parotid ducts. The ducts were fitted with non-obstructive sampling catheters through their oral ends. After probe encapsulation (8 days), salivary flows were continuously recorded (4-5 days, dual-channel ultrasonic flowmeter). For rumination, eating, resting and drinking periods, respectively, the parotid daily outputs recorded were 1 96 + 0 57, 0 97 + 0 34, 2 84 + 0 41 and < 004 1 and bilateral flow rates were 6 76 + 0 70, 5 63 + 1.42, 2 50 + 0 58 and 1 69 + 0 88 ml min-'. An ipsilateral secretory reflex was evident when the sheep changed chewing side during rumination (4.44 + 0*96 ml min-1 ipsilateral vs. 2 63 + 0.90 ml min-' contralateral flow, P < 0 01). Secretory patterns are described in detail during rest, eating, drinking and rumination periods. The pH of parotid saliva (8.36 + 0.14) and the osmolality (273.8 + 9 9 mosmol kg-') were independent of secretory rates. In situ probe calibration showed high accuracy (0-9 %). The main advantages of the technique are its accuracy and good tolerance, duct integrity and maintenance of nervous supply, minimal surgery, uninterrupted salivary flow, simultaneous bilateral measurements and precise flow monitoring, permitting detailed observations.

To test the hypothesis that urea can be recycled from the renal pelvis, [14C]urea diluted in native urine (1 microCi/ml) was perfused (0.5 ml/min) into one of the pelvises of sheep fed either normal (NP) or low (LP)-protein diets. Blood samples were obtained from the ipsilateral renal vein and from the carotid artery throughout the perfusions. 14C activity determinations in urine and plasma demonstrated a flux of [14C]urea from the pelvis to renal vein blood (40,000 in NP and 130,000 disintegrations/min in LP sheep, P less than 0.01). The corresponding flux of native urea was only 1.5 times higher in NP than in LP sheep (6.8 +/- 1.1 vs. 4.7 +/- 2.9 mumol/min, not significant) despite their 8 times higher urinary concentration of urea. The fraction of filtered urea that was reabsorbed in the pelvis was larger in LP sheep (7.5 +/- 3.7 vs. 1.9 +/- 0.7% in NP sheep, P less than 0.05). A fraction of urea is thus actually recycled from the renal pelvis in sheep, and this pelvic retention is enhanced in LP animals. The importance of this phenomenon in the nitrogen economy is discussed.

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To determine whether non-fibrous carbohydrate (NFC) supplementation improves fiber digestibility and microbial protein synthesis, 18 Corriedale ewes with a fixed intake level (40 g dry matter (DM)/kg BW 0.75 ) were assigned to three (n 5 6) diets: F 5 100% fresh temperate forage, FG 5 70% forage 1 30% barley grain and FGM 5 70% forage 1 15% barley grain 1 15% molasses-based product (MBP, Kalori 3000). Two experimental periods were carried out, with late (P1) and early (P2) vegetative stage forage. For P2, ewes were fitted with ruminal catheters. Forage was distributed at 0900 h, 1300 h, 1800 h and 2300 h, and supplement added at 0900 h and 1800 h meals. Digestibility of the different components of the diets, retained N and rumen microbial protein synthesis were determined. At the end of P2, ruminal pH and N-NH 3 concentration were determined hourly for 24 h. Supplementation increased digestibility of DM ( P , 0.001) and organic matter (OM; P , 0.001) and reduced NDF digestibility ( P 5 0.043) in both periods, with greater values in P2 ( P 5 0.008) for the three diets. Daily mean ruminal pH differed ( P , 0.05) among treatments: 6.33 (F), 6.15 (FG) and 6.51 (FGM). The high pH in FGM was attributed to Ca(OH) 2 in MBP. Therefore, the decreased fiber digestibility in supplemented diets could not be attributed to pH changes. The mean ruminal concentration of N-NH 3 was 18.0 mg/dl, without differences among treatments or sampling hours. Microbial protein synthesis was greater in P2 (8.0 g/day) than in P1 (6.1 g/day; P 5 0.006), but treatments did not enhance this parameter. The efficiency of protein synthesis tended to be lower in supplemented groups (16.4, 13.9 and 13.4 in P1, and 20.8, 16.7 and 16.2 g N/kg digestible OM ingested in P2, for F, FG and FGM, respectively; P 5 0.07) without differences between supplements. The same tendency was observed for retained N: 2.55, 1.38 and 1.98 in P1, and 2.28, 1.23 and 1.10 g/day in P2, for F, FG and FGM, respectively; P 5 0.05). The efficiency of microbial protein synthesis was greater in P2 (P 5 0.007). In conclusion, addition of feeds containing NFCs to fresh temperate forage reduced the digestibility of cell walls and did not improve microbial protein synthesis or its efficiency. An increase in these parameters was associated to the early phenological stage of the forage.

The effect of glucagon on renal haemodynamics in sheep is controversial. In this study we have examined the effects of perfused glucagon on renal blood flow (RBF) in six conscious sheep bilaterally implanted with transit‐time ultrasonic flow metering probes around the renal arteries. Glucagon was perfused intravenously over 90 min at doses of 3.12, 6.25, 12.5, 25, 50 and 100 ng kg−1 min−1. Mean RBF was calculated over 10 min periods. Blood samples were taken to monitor the time course of the changes in glycaemia and glucagonaemia. The perfusions of glucagon induced rapid and progressive dose‐dependent increases in RBF (9‐19.2 %, P < 0.05) and glycaemia (29‐155 %, P < 0.05) for doses of 25‐100 ng kg−1 min−1. High positive correlations were found between the increases in RBF and glucagonaemia (R2= 0.95) and between the increases in RBF and glycaemia (R2= 0.96). At the lowest doses of glucagon (3.12‐12.5 ng kg−1 min−1), the increase in RBF was highly significant; however, the rise in glucose level was not. At the highest doses (25‐100 ng kg−1 min−1) the time course of the changes in RBF was parallel to that of glucagonaemia throughout the perfusion time. However, between minutes 45 and 90 of the glucagon perfusion, the increase in RBF was the inverse of the change in glycaemia, which decreased. One hour after the end of the 50 and 100 ng kg−1 min−1 perfusions, the glucose levels were still significantly higher than the baseline, while the RBF values were not. These results are consistent with the idea that the enhanced RBF cannot be attributed to a rise in blood glucose level. They also show that the haemodynamic response to glucagon perfusion was more sensitive than the metabolic response. It is concluded that the intravenous perfusion of physiological doses of glucagon induced a highly sensitive dose‐dependent increase in RBF in sheep.